Method for predicting degree of corrosion of weather-resistant steel

ABSTRACT

A predicted corrosion amount of a painted or unpainted atmospheric corrosion resistant steel is calculated by using extrinsic corrosion information including weather observation data, an amount of airborne salt, and an amount of sulfur oxide in a planned location for use where the atmospheric corrosion resistant steel is to be used, and intrinsic corrosion information on components of the atmospheric corrosion resistant steel. The weather observation data on this occasion preferably includes the annual wetness time, annual mean wind speed, and annual mean temperature. Moreover, it is preferable to calculate a corrosivity index, estimate a first-year corrosion amount of the atmospheric corrosion resistant steel and a rust stabilization index from the corrosivity index, and calculate a corrosion amount accumulated over time.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a national stage application of PCT Application No.PCT/JP02/07037 which was filed on Jul. 11, 2002, and published on Jan.23, 2003 as International Publication No. WO 03/006957 (the“International Application”). This application claims priority from theInternational Application pursuant to 35 U.S.C. § 365. The presentapplication also claims priority under 35 U.S.C. § 119 from JapanesePatent Application Nos. 2001-212764 and 2001-342763, filed on Jul. 12,2001 and Nov. 8, 2001, respectively, the entire disclosures of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method for predicting an amount ofcorrosion of an atmospheric corrosion resistant steel, which issubjected to surface treatment such as rust stabilization treatment,painting or plating, and maintenance management such as inspection,repair or cleaning as required, and a method for selecting a steel typeto which the aforementioned method is applied.

BACKGROUND OF THE INVENTION

Atmospheric corrosion resistant steels have been applied to many actualstructures including bridges because of its unique property ofpreventing rust by rust. There are many cases where a reduction inmaintenance management costs is attained by using this steel materialwith its functions utilized to the full. On the other hand, a problemsometimes arises when the atmospheric corrosion resistant steel iscarelessly used in coastal regions and the like where there is a lot ofairborne salt. In recent years, in inland regions as well, localformation of abnormal rust due to the spraying of thawing salt issometimes found.

As is represented by the minimum maintenance bridge concept proposed bythe Ministry of Land, Infrastructure and Transport of Japan, futurestructures including bridges are requested to employ atmosphericcorrosion resistant steels, surface treatment technology, structuraldesign methods, and the like which can be actually used reliably for avery long period while achieving a further reduction in maintenance andmanagement costs. Therefore, as a form of 21st century typeinfrastructure which maintains and develops cost-competitiveness withAsian countries as our country as a whole, rust science study andapplication technology development related to the atmospheric corrosionresistant steel capable of realizing Life Cycle Cost (“LCC”) minimum aregreatly expected.

Against this background, in the Japan Society of Corrosion Engineering,the Rust Science Workshop which supports 21st century infrastructure wasorganized for four years from 1997. Many specialists enthusiasticallydiscussed the concept of “stable rust” heretofore very confused as basicunderstanding to use atmospheric corrosion resistant steels moresecurely and safely.

As a result, the following suggestion has been issued as the opinion ofthe Society in the 132nd Corrosion Engineering Symposium sponsored bythe Japan Society of Corrosion Engineering held on Jun. 25, 2001 (JapanSociety of Corrosion Engineering, Rust Science Workshop: Referencematerials for the 132nd Corrosion Engineering Symposium “New Developmentof Rust Science to Realize Minimum Maintenance Bridge Concept”, p 3,Jun. 25, 2001).

“Rust stabilization” of the atmospheric corrosion resistant steel meansa state in which the corrosion rate has reduced to the extent that thesecular deterioration of the load carrying capacity of a structure isinsignificant from an engineering viewpoint (0.01 mm/year or less as astandard).

As provisional interpretation: the stable rust is rust formed when ruston the atmospheric corrosion resistant steel is “stabilized”. However,although the aforementioned state is defined as “rust stabilization”,since the term of stable rust has a strong physical image, it isdesirable to withhold the scientific use of this term. As an alternativematerial term, the term of protective rust is used for rust having ahigh protective function.

Rust when “stabilized” is characterized in that although a sufficientperiod (e.g., five years or more) has elapsed, the rust does not growthick (except a case where traces of exfoliated rust are left).

One of the important messages in this suggestion is the definition of“rust stabilazation” of the atmospheric corrosion resistant steel.Namely, when the industrial material called an atmospheric corrosionresistant steel is used for a structure, the realization of “a ruststabilization state” in which the load carrying capacity of thestructure using this material can exist stably over a long period isrecognized anew as a higher objective concept than other variousarguments about what the matter called stable rust is. Moreover, thedevelopment of the technology of predicting the accumulated amount ofcorrosion of the atmospheric corrosion resistant steel over a longperiod of time is suggested as one of the most important items inmaterial selection, structural design, and maintenance/management.

Conventionally, among methods for predicting an accumulated corrosionamount of an atmospheric corrosion resistant steel over a long period oftime which are generally performed, there is a method of performing anexposure test over a period of approximately ten years in a constructionsite or under atmospheric environmental conditions similar to those ofthe construction site, finding a value A and a value B by fitting asecular change of a corrosion loss obtained in this period to arelational expression of (amount of corrosion)=A×(exposure period)^(B),and calculating a corrosion loss over any given long period of time withthese values (see, for example, Public Works Research Institute of theMinistry of Construction, the Kozai Club, Japan Association of SteelBridge Construction: Collaborative Research Report on Application ofAtmospheric corrosion resistant steel to Bridges (XII), p 20, March,1992).

However, in this predicting method, the exposure test in actualatmospheric environment over a period of approximately ten years isnecessary to obtain constant terms, the value A and the value B, andfunds, labor, and time are needed before a judgment is made. Hence, aproblem that the market competitiveness of a technical business methodadopted at present of the atmospheric corrosion resistant steel isweaker than that of concrete structures and the like which compete withthe atmospheric corrosion resistant steel is indicated.

As for a flow concerning judgment on the applicability of theatmospheric corrosion resistant steel, flows such as shown in FIG. 1 toFIG. 4 are disclosed in Japanese Patent Laid-open No. 2000-1816 and soon. However, in each flow, only factors which contribute to the amountof corrosion in the usage environment are substantially arranged, and noquantitative criterion for judging the propriety of use of a steel typeto be applied based on a predicted corrosion amount in an adaptiveenvironment is proposed or disclosed. Namely, these flows are noteffective solutions for a demand for a more quantitative judgment methodbased on the predicted corrosion amount. Moreover, these flows have aproblem that the amount of sulfur oxide and the annual wetness timewhich are important parameters for the prediction of the corrosionamount are not considered at all.

In the conventional method for predicting long-term corrosion/wear ofthe atmospheric corrosion resistant steel, exposure test data in theconstruction site or exposure test data in an atmospheric environmentsimilar to the construction site are indispensable, and to obtain thedata, high expenses of test/analysis are needed. Further, regions whereunpainted atmospheric corrosion resistant steels are used for roadbridges in our country are limited to regions where the amount ofairborne salt is 0.05 mdd or less (mdd is a brevity code of mg/dm²day),but in some cases, abnormality does not occur to the atmosphericcorrosion resistant steel even under the environmental condition of anairborne salt amount of 0.05 mdd or more. Therefore, there are somecases where an opportunity to reduce the maintenance cost is missedbecause the applicability is judged only with a single index.Furthermore, when the atmospheric corrosion resistant steel is usedbeyond the limit of application without sufficient prediction ofcorrosion/wear behavior, partial abnormal corrosion occurs, which causesunexpected repairing expenses.

As described above, no solution which associates corrosivity ofenvironmental condition with rust stabilization performance of theatmospheric corrosion resistant steel exists, and hence it is said thatthe application of the atmospheric corrosion resistant steel entailshigh risks and high returns.

SUMMARY OF THE INVENTION

In view of the aforementioned situation, a technology has beenresearched for judging the applicability of an atmospheric corrosionresistant steel at low cost, speedily, and with high precision isindispensable. In addition, method has been reviewed for predicting along-term corrosion loss of an atmospheric corrosion resistant steel bycalculation based on weather data, airborne salt amount data, and sulfuroxide amount data in the vicinity of a construction site.

One of the objects of the present invention is to provide a method forpredicting an amount of corrosion of an atmospheric corrosion resistantsteel capable of solving the aforementioned problems of prior arts andjudging the applicability of the atmospheric corrosion resistant steelat low cost, speedily, and with high precision.

As a result of a comprehensive research and study in order to solve theaforementioned problems, a natural phenomenon called the ruststabilization of an atmospheric corrosion resistant steel has beenarranged, so as to construct a calculation technology philosophy ofpredicting a long-term corrosion/wear amount. Such calculationtechnology philosophy can be embodied in the form of software.

A method for predicting an amount of corrosion of an atmosphericcorrosion resistant steel according to the present invention may includea calculation of a predicted corrosion amount of the atmosphericcorrosion resistant steel using extrinsic corrosion informationincluding weather observation data, an amount of airborne salt, and anamount of sulfur oxide in a planned location for use where theatmospheric corrosion resistant steel is to be used, and intrinsiccorrosion information on components of the atmospheric corrosionresistant steel, with an electronic calculator.

A system for predicting a corrosion amount according to an exemplaryembodiment of the present invention may include an input arrangement forreceiving information. The system may also include a computingarrangement which is configured to calculate a predicted corrosionamount of an atmospheric corrosion resistant steel with extrinsiccorrosion information including weather observation data, an amount ofairborne salt, and an amount of sulfur oxide in a planned location foruse where the atmospheric corrosion resistant steel is to be used, andintrinsic corrosion information on components of the atmosphericcorrosion resistant steel which are received from the input arrangement.Further, the system according to the present invention can include anoutput arrangement which is adapted to output a result of thecalculation by the computing arrangement.

The atmospheric corrosion resistant steel subject to the system andmethod of the present invention may includes a hot-rolled atmosphericcorrosion resisting steel for welded structure (symbol: SMA) stipulatedby JIS G 3114 and a super atmospheric corrosion resisting rolled steel(symbol: SPA-H, SPA-C) stipulated by JIS G 3125. Such steel can alsoincludes an atmospheric corrosion resistant steel containingapproximately 1–3 mass % of Ni, for example, as disclosed in JapanesePatent Application No. 5-51668, Japanese Patent Application No.7-207340, Japanese Patent Application No. 7-242993, Japanese PatentApplication No. 8-134587, Japanese Patent Application No. 11-71632,Japanese Patent Application No. 11-172370, the entire disclosures ofwhich are incorporated herein by reference. The atmospheric corrosionresistant steel subject to the exemplary embodiments of the presentinvention also includes a coastal/seaside atmospheric corrosionresistant steel containing Mo, Cu. Ti, Cr, and so on, which has beenrecently developed.

The weather observation data is data obtained by observing weatherconditions under which the atmospheric corrosion resistant steel isexposed. For example, the weather observation data may include data onan annual wetness time TOW (h), an annual mean temperature T (° C.), anannual mean wind speed W (m/sec.), and so on.

The amount of airborne salt is a value obtained by a particular methodbased on a method for measuring the amount of sea salt particlesstipulated by Reference 3 of JIS Z 2381 (i.e., General requirements foroutside exposure test method). In particular, a gauze which is driedwell after thoroughly leaching out salt by pure water is folded in twoand fitted into a wooden frame with an inside dimension of 100 mm×100mm. Then, the gauze is exposed vertically for one month in awell-ventilated place which is not directly exposed to the rain, takenoff after the exposure, and analyzed to find the amount of NaCl. Thevalue obtained by expressing the amount of in NaCl in NaCl·mg/dm²/day(brevity code: mdd) is the amount of airborne salt. On this occasion,attention needs to be paid to conversion into the amount of adhesion onone side. This data is widely used as an index indicating how much saltis contained in atmospheric environment such as a construction site andat what speed the salt adheres to a structure or the like.

An exemplary amount of sulfur oxide can be a value obtained by aparticular method based on a method for measuring the amount of sulfuroxide stipulated by Reference 2 of JIS Z 2381 (i.e., Generalrequirements for outside exposure test method). In particular, acylinder made of plastic or the like, on which gauze coated with a leaddioxide paste is put, is exposed vertically for one month in a dedicatedshelter. After the exposure, the cylinder is removed and analyzed. Thevalue obtained by expressing the amount of SO₂ in SO₂·mg/dm²day (brevitycode: mdd) is the amount of sulfur oxide. This data is widely used as anindex indicating how much sulfur oxide such as sulfur acid gas iscontained in atmospheric environment such as a construction site and atwhat speed the sulfur oxide adheres to a structure or the like.

It should be understood that measurement values correlated with thesevalues can be determined by methods other than JIS Z 2381, such as anISO method and a direct measurement method of attached salt. If themeasurement methods are different, the values may also differ accordingto a difference between their capture rates, but it should be understoodthat if the values are converted into an airborne salt amount and asulfur oxide amount based on the aforementioned JIS method, the valuescan be applied to the method for predicting the amount of corrosion ofthe atmospheric corrosion resistant steel associated with the exemplaryembodiments of the present invention.

The aforementioned exemplary method for predicting the amount ofcorrosion of the atmospheric corrosion resistant steel according to thepresent invention can be effectively performed by utilizing a computerto make the calculation. Therefore, as for the distribution thereof, themethod according to present invention may be provided on a computerreadable record medium, can also be downloaded from the medium via anelectric communication line, such as the Internet.

An exemplary embodiment of a computer readable record medium accordingto the present invention may include a program thereon. The program cancause a computer to calculate a predicted corrosion amount withextrinsic information including weather observation data, an amount ofairborne salt, and an amount of sulfur oxide in a planned location foruse where an atmospheric corrosion resistant steel is to be used, andintrinsic corrosion information on components of the atmosphericcorrosion resistant steel.

Further, the method of the present invention may be implemented by acomputer. According to one exemplary embodiment of the method forselecting a steel type according to the present invention, a predictedcorrosion amount of each of atmospheric corrosion resistant steels withextrinsic corrosion information can be calculated, including weatherobservation data, an amount of airborne salt, and an amount of sulfuroxide in a planned location for use where the atmospheric corrosionresistant steel is to be used, and intrinsic corrosion information oncomponents of one or more than one type of atmospheric corrosionresistant steel planned to be used, by an electronic calculator. Inaddition, the predicted corrosion amount and a design permissiblecorrosion amount may be compared in a design life period using acalculating arrangement (e.g., an electronic calculator).

Another exemplary embodiment of a system for selecting a steel typeaccording to the present invention can include an input which isconfigured to obtain information, and a computing arrangement which isprogrammed to calculate a predicted corrosion amount of each ofatmospheric corrosion resistant steels with extrinsic corrosioninformation including weather observation data, an amount of airbornesalt, and an amount of sulfur oxide in a planned location for use wherethe atmospheric corrosion resistant steel is to be used, and intrinsiccorrosion information on components of one or more than one type ofatmospheric corrosion resistant steel planned to be used which areinputted from the input means. Such exemplary system may also include acomparing arrangement which is adapted to compare the predictedcorrosion amount and a design permissible corrosion amount in a designlife period, and an output arrangement which can be adapted to output aresult of the comparison.

Another exemplary embodiment of the method for maintaining and managinga steel structure according to the present invention may include thesteps of: finding an actually measured first-year corrosion amount froman actual measurement result of a corrosion loss in any given period ofan actual structure made of an atmospheric corrosion resistant steel ora corrosion loss in any given period of a vertical exposure member or ahorizontal exposure member which is made of the atmospheric corrosionresistant steel and attached to the actual structure; predicting acorrosion amount of the atmospheric corrosion resistant steel with anelectronic calculator with the actually measured first-year corrosionamount as A_(V)or A_(H); and determining a maintenance management policybased on the predicted corrosion amount of the atmospheric corrosionresistant steel.

Another embodiment of the method for maintaining and managing a steelstructure according to the present invention includes the steps of:finding an actually measured first-year corrosion amount from an actualmeasurement result of a corrosion loss in any given period of an actualstructure made of an atmospheric corrosion resistant steel or acorrosion loss in any given period of a vertical exposure member or ahorizontal exposure member which is made of the atmospheric corrosionresistant steel and attached to the actual structure; calculating acorrosivity index Z by the undermentioned equation (Eq. 6) fromextrinsic corrosion information including weather observation data, anamount of airborne salt, and an amount of sulfur oxide in a locationwhere the actual structure is installed, and intrinsic corrosioninformation on components of the atmospheric corrosion resistant steel,with an electronic calculator; estimating a first-year corrosion amountof the atmospheric corrosion resistant steel from the corrosivity indexZ with the electronic calculator; comparing the actually measuredfirst-year corrosion amount and the estimated first-year corrosionamount with the electronic calculator; correcting the corrosivity indexZ based on a result of the comparison with the electronic calculator;predicting a corrosion amount of the atmospheric corrosion resistantsteel based on the corrected corrosivity index Z with the electroniccalculator; and determining a maintenance management policy based on thepredicted corrosion amount.

Another embodiment of the system for maintaining and managing a steelstructure according to the present invention includes an inputarrangement which can receive information, and a computing arrangementwhich is configured to respectively calculate actually measuredfirst-year corrosion amounts of a vertical exposure member and ahorizontal exposure member which are made of an atmospheric corrosionresistant steel based on actual measurement results of corrosion lossesin any given period of the vertical exposure member and the horizontalexposure member made of the atmospheric corrosion resistant steel whichare inputted from the input arrangement, calculating a predictedcorrosion amount of the atmospheric corrosion resistant steel withextrinsic information including weather observation data, an amount ofairborne salt, and an amount of sulfur oxide in a planned location foruse where the atmospheric corrosion resistant steel is to be used whichis received from the input arrangement, intrinsic corrosion informationon components of the atmospheric corrosion resistant steel obtained viathe input arrangement, and the respective actually measured first-yearcorrosion amounts, and determining a maintenance management policy basedon the predicted corrosion amount.

An exemplary method for providing information on an atmosphericcorrosion resistant steel according to the present invention includesthe steps of: a user accessing a server for calculating a predictedcorrosion amount of an atmospheric corrosion resistant steel withenvironmental data including weather observation data, an amount ofairborne salt, and an amount of sulfur oxide, and intrinsic corrosioninformation on components of the atmospheric corrosion resistant steelfrom a terminal device via an electric communication line; the userinputting environmental data including weather observation data, anamount of airborne salt, and an amount of sulfur oxide in a plannedlocation for use where an atmospheric corrosion resistant steel is to beused from the terminal device to the server; the user permitting theserver to recognize intrinsic corrosion information on components of oneor more than one atmospheric corrosion resistant steel planned to beused from the terminal device; the server calculating a predictedcorrosion amount of each of the atmospheric corrosion resistant steelsbased on the environmental data and the intrinsic corrosion information;the server transmitting the predicted corrosion amount to the terminaldevice via the electric communication line; and the terminal deviceoutputting the predicted corrosion amount.

An exemplary system for providing information on an atmosphericcorrosion resistant steel according to the present invention may includea server, which is accessible to a user from a terminal device via anelectric communication line, programmed to calculate a predictedcorrosion amount of an atmospheric corrosion resistant steel withenvironmental data including weather observation data, an amount ofairborne salt, and an amount of sulfur oxide, and intrinsic corrosioninformation on components of the atmospheric corrosion resistant steel,and to transmit the predicted corrosion amount to the terminal devicevia the electric communication line.

An exemplary method for an atmospheric corrosion resistant steelaccording to the present invention includes the steps of: a useraccessing a server for calculating a predicted corrosion amount of anatmospheric corrosion resistant steel with environmental data includingweather observation data, an amount of airborne salt, and an amount ofsulfur oxide, and intrinsic corrosion information on components of theatmospheric corrosion resistant steel from a terminal device via anelectric communication line; the user inputting environmental dataincluding weather observation data, an amount of airborne salt, and anamount of sulfur oxide in a planned location for use where anatmospheric corrosion resistant steel is to be used from the terminaldevice to the server; the user permitting the server to recognizeintrinsic corrosion information on components of one or more than oneatmospheric corrosion resistant steel planned to be used from theterminal device; the server calculating a predicted corrosion amount ofeach of the atmospheric corrosion resistant steels based on theenvironmental data and the intrinsic corrosion information; the servertransmitting the predicted corrosion amount to the terminal device ofthe user via the electric communication line; the terminal deviceoutputting the predicted corrosion amount; and determining a businesscounterpart based on at least one type of element selected from thegroup consisting of the presence or absence of history of access to theserver and the frequency of access to the server.

Another exemplary method for an atmospheric corrosion resistant steelaccording to the present invention includes the steps of: a userinputting extrinsic corrosion information including weather observationdata, an amount of airborne salt, and an amount of sulfur oxide in aplanned location for use where a customer plans to use an atmosphericcorrosion resistant steel to an electronic calculator for calculating apredicted corrosion amount of an atmospheric corrosion resistant steelwith extrinsic corrosion information including weather observation data,an amount of airborne salt, and an amount of sulfur oxide and intrinsiccorrosion information on components of the atmospheric corrosionresistant steel; the user permitting an electronic arrangement torecognize intrinsic corrosion information on components of one or morethan one type of atmospheric corrosion resistant steel which thecustomer plans to use; the electronic calculator calculating a predictedcorrosion amount of each of the atmospheric corrosion resistant steels;and the user presenting a result of the calculation to the customer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing an example of a conventional method fordetermining the applicability of an atmospheric corrosion resistantsteel;

FIG. 2 is a flowchart showing another example of the conventional methodfor determining the applicability of the atmospheric corrosion resistantsteel;

FIG. 3 is a flowchart showing still another example of the conventionalmethod for determining the applicability of the atmospheric corrosionresistant steel;

FIG. 4 is a flowchart showing yet another example of the conventionalmethod for determining the applicability of the atmospheric corrosionresistant steel;

FIG. 5 is a flowchart showing a method for predicting the amount ofcorrosion and a method for judging the applicability of an atmosphericcorrosion resistant steel based on an exemplary embodiment of a methodaccording to the present invention;

FIG. 6 is a diagram illustrating a concept of a rust stabilizationstate;

FIG. 7 is a diagram schematically showing a relation between a corrosionamount accumulated over time Y and the number of years elapsed X basedon Eq. (4) with two logarithmic axes;

FIG. 8 is a diagram showing a relation between an airborne salt amount Cand a first-year corrosion amount A;

FIG. 9 is a diagram showing the relation between a corrosivity index Zand the first-year corrosion amount A of a vertical exposure member;

FIG. 10 is a diagram showing a relation between the corrosivity index Zand the first-year corrosion amount A of a horizontal exposure member;

FIG. 11 is a diagram showing a relation between the first-year corrosionamount A and a stabilization index B and its interpretation;

FIG. 12 is a chart showing an example of a panel for setting conditionsof long-term corrosion/wear prediction software for an atmosphericcorrosion resistant steel;

FIG. 13 is a chart showing an example of a panel for obtaining longitudeand latitude of the long-term corrosion/wear prediction software for theatmospheric corrosion resistant steel;

FIG. 14 is a chart showing an example of a panel for obtaining weatherdata of the long-term corrosion/wear prediction software for theatmospheric corrosion resistant steel;

FIG. 15 is a chart showing an example of the panel for settingconditions of the long-term corrosion/wear prediction software for theatmospheric corrosion resistant steel the input to which is completed;

FIG. 16 is a chart showing an example of a panel displaying a first-yearcorrosion amount A and a rust stabilization index B of the long-termcorrosion/wear prediction software for the atmospheric corrosionresistant steel;

FIG. 17 is a chart showing an example of a panel for viewing an overviewof calculation results of the long-term corrosion/wear predictionsoftware for the atmospheric corrosion resistant steel;

FIG. 18 is a chart showing an example of a panel for viewing calculationresults of long-term corrosion/wear prediction when a bare JIS typeatmospheric corrosion resistant steel is used;

FIG. 19 is a chart showing an example of a panel graphically displayingcalculation result of long-term corrosion/wear prediction of a coastalatmospheric corrosion resistant steel with excessive influence takeninto consideration;

FIG. 20 is a chart showing an example of a panel graphically displayingcalculation results of long-term corrosion/wear prediction when the JIStype atmospheric corrosion resistant steel is subjected to generalsurface treatment;

FIG. 21 is a chart showing an example of a panel graphically displayingcalculation results of long-term corrosion/wear prediction when the JIStype atmospheric corrosion resistant steel is subjected to surfacetreatment for the atmospheric corrosion resistant steel;

FIG. 22 is a chart showing an example of a panel graphically displayingcalculation result of long-term corrosion/wear prediction by a method ofrepainting the JIS type atmospheric corrosion resistant steel by thegeneral surface treatment;

FIG. 23 is a chart showing an example of conditions provided to a usageenvironment conditions setting panel in a portion of a structure aroundwhich the amount of airborne salt is assumed to be relatively small in abridge structure to be constructed;

FIG. 24 is a chart showing an example of a corrosion/wear predictioncurve calculated under the conditions in FIG. 23 in the portion of thestructure around which the amount of airborne salt is assumed to berelatively small;

FIG. 25 is a chart showing an example of conditions inputted to theusage environment conditions setting panel in a portion of the structurearound which the amount of airborne salt is assumed to be relativelylarge and the humidity is assumed to be high in the bridge structure tobe constructed;

FIG. 26 is chart showing an example of a corrosion/wear prediction curvecalculated under the conditions in FIG. 25 in the portion of thestructure around which the amount of airborne salt is assumed to berelatively large and the humidity is assumed to be high;

FIG. 27 is a chart showing an example of a corrosion/wear predictioncurve calculated under the conditions in FIG. 25 in the portion of thestructure around which the amount of airborne salt is assumed to berelatively large and the humidity is assumed to be high and which issubjected to the rust stabilization surface treatment for theatmospheric corrosion resistant steel;

FIG. 28 is a diagram schematically showing an example of a method forproviding information on the atmospheric corrosion resistant steel basedon the method for predicting corrosion according to the embodiment ofthe present invention; and

FIG. 29 is a block diagram showing an example of a processing systemcapable of performing exemplary steps shown in FIG. 5.

DETAILED DESCRIPTION

FIG. 5 illustrates a flowchart for an exemplary embodiment of a methodaccording to an embodiment of the present invention for predicting anamount of corrosion and a method for judging the applicability of anatmospheric corrosion resistant steel. FIG. 29 shows a block diagram ofan exemplary embodiment of a processing system according to the presentinvention which is capable of performing steps shown in FIG. 5.

In the processing system shown in FIG. 29, information, for example, onthe amount of airborne salt, the amount of sulfur oxide, and regionalweather data in FIG. 5 is inputted to a computing part 2 via aninformation inputting part (input means) 1. The information inputtingpart 1 may be a keyboard for a personal computer or the like, or aninterface board for an electrical communication line or the like. Thecomputing part (computing means) 2 performs a computation such as thecalculation of a first-year corrosion amount, calculation of a ruststabilization index, correction of a value A and a value B, andprediction of a corrosion amount accumulated over time. A display part(display unit) 3 displays, for example, information outputted from thecomputing part 2. Note that not only the display part 3 but also aprinter, for example, may be provided as an output means. A comparingpart 4 compares a corrosion amount and a permissible value for judgingwhether a corrosion amount in a design life period in FIG. 5 is thepermissible value or less.

FIG. 6 shows an exemplary concept which may be used as a background ofthe aforementioned definition (proposal) of rust stabilization. As shownin FIG. 6, the corrosion itself does not progress if environmentalconditions are sufficiently mild, whereby the protective function ofrust is hardly enhanced, but the load carrying capacity of the structurebecomes stable over a long period of time. If the environmentalconditions become severe, protective rust may be formed by the effect ofalloy components, and thanks to its corrosion inhibiting effect, theload carrying capacity of the structure becomes stable over a longperiod of time. Either of the aforementioned states can be regarded as“a normal state” for the atmospheric corrosion resistant steel from theviewpoint of load carrying capacity. Accordingly, this state can berepresented by “a rust stabilization state”. On the other hand, if theenvironmental conditions become severer, the corrosion inhibiting effectreaches its limit even if the protective rust is temporarily formed,sometimes leading to “an abnormal state” for the atmospheric corrosionresistant steel such as the occurrence of accelerated corrosion. A limitpoint at which the normal state cannot be maintained any longer iscalled a rust stabilization limit condition.

An analysis using the basic concept of the corrosion phenomenon of theatmospheric corrosion resistant steel can be pursued based on FIG. 6 infundamental principal. First, when the atmospheric corrosion resistantsteel is exposed to an environment within the rust stabilization limitcondition, in which the atmospheric corrosion resistant steel issubjected to repetition of moderate dryness/wetness, a secular reductionin corrosion rate occurs according to the formation of protective rust.In order to model this situation, if the number of years elapsed istaken as X, a corrosion rate V_(x) after X year(s) can be represented byan equation (Eq. 1) with a corrosion rate V₁ and an index β when thenumber of years elapsed is one. According to this equation (Eq. 1), thecorrosion rate when X=0 is infinite, but since this corrosion rate is atheoretical corrosion rate on the assumption that this state is a statein which the steel is totally uncoated, that is, a state in which thesteel is not coated even with a passive film, for example, immediatelyafter the steel has been subjected to shot blast, this is insignificantfrom an engineering viewpoint.

$\begin{matrix}{v_{x} = {v_{1} \cdot \frac{1}{X^{\beta}}}} & \left( {{Eq}.\mspace{14mu} 1} \right)\end{matrix}$

If both sides of the equation (Eq. 1) are integrated with respect to X,an accumulated corrosion amount Y after X years can be found, and anequation (Eq. 2) may be obtained.

$\begin{matrix}{Y = {{\int_{x = 0}^{x}{v_{x}{\mathbb{d}X}}} = {\frac{v_{1}}{1 - \beta}X^{1 - \beta}}}} & \left( {{Eq}.\mspace{14mu} 2} \right)\end{matrix}$

In this manner, if the amount of first-year corrosion (first-yearcorrosion amount) is taken as A as an initial condition, the value of Ais represented by an equation (Eq. 3).

$\begin{matrix}{A = {Y_{({x = {1{({year})}}})} = {{\int_{x = 0}^{1}{v_{x}{\mathbb{d}X}}} = \frac{v_{1}}{1 - \beta}}}} & \left( {{Eq}.\mspace{14mu} 3} \right)\end{matrix}$

Moreover, by letting 1−B

β=B and calling the value of B as a stabilization index, a predictionformula of the corrosion amount accumulated over time of the atmosphericcorrosion resistant steel which is empirically well-known can beobtained by substituting the equation (Eq. 3) in the equation (Eq. 2).Y=AX ^(B)  (Eq. 4)

FIG. 7 shows the relation of logarithms on both sides of the equation(Eq. 4). As shown in FIG. 7, there is a linear relationship between logXand logY, and to predict Y accurately, it is indispensable to estimatethe first-year corrosion amount A and the rust stabilization index Bwith sufficient precision. In particular, as for the atmosphericcorrosion resistant steel, when long-term usage is taken intoconsideration, the value of the rust stabilization index B with linearinclination taken according to the stabilization of rust formed on thesurface is an important factor.

Further, the result of the study of the equation (Eq. 4) in relation toFIG. 6 is as follows. When the severity of a corrosive environment islow, the rust stabilization index B takes a value almost close to one,and corrosion progresses almost in accordance with a linear rule.However, since the first-year corrosion amount A is extremely small, thecorrosion rate is very slow, leading to the realization of the ruststabilization state in which the secular deterioration of load carryingcapacity of the structure is insignificant from an engineeringviewpoint.

As the severity of the corrosive environment becomes higher gradually,the first-year corrosion amount A becomes larger, but the ruststabilization index B becomes smaller since the formation of protectiverust is promoted. As a result, the rust stabilization state thanks to asecular reduction in corrosion rate can be realized. When the severityof the corrosive environment further increases, the protectiveness ofrust is lost, thereby both the first-year corrosion amount A and therust stabilization index B increase, and consequently abnormal corrosionoccurs in a severe corrosive environment beyond the rust stabilizationlimit condition.

When it is thought that the corrosion rate in a state in which theprotectiveness of rust is low is determined by the environmentalconditions and the corrosion resistance of a steel material, thefirst-year corrosion amount A can be approximately expressed byfunctions of an equation (Eq. 5).A=F(Z)·G(w)  (Eq. 5)

where Z is an atmospheric corrosivity index, w is a corrosion resistanceindex of the steel material, F(Z) and G(w) are functions representingthe contribution of the corrosivity index Z and the corrosion resistanceindex w to the first-year corrosion amount A. If components of the steelmaterial are determined, the corrosion resistance index G(w) is fixed,whereby it becomes a subject of discussion how the corrosivity index Zis found and then related to the first-year corrosion amount A.

The environmental conditions are generally considered to be complexincluding many factor changes. Until now, the environmental conditionsunder which the atmospheric corrosion resistant steel is used is firstapproximately set by the amount of airborne salt, but even under anenvironment with an airborne salt amount beyond 0.05 mdd, theatmospheric corrosion resistant steel sometimes is in a good ruststabilization state. Hence, there is an objection to the way in whichits applicability condition is determined only by a single index. On theother hand, there is an example in which the correlation between variouspieces of weather data and the corrosion rate is statistically analyzed,but a sufficient conclusion is not necessarily obtained. One of reasonsfor this is that no study is made in terms of chemical kinetics.

Hence, the corrosivity of an atmospheric environment is studied on thebasis of the aforementioned arguments. A hypothetical way of thinkingfor deriving a corrosivity index of the atmospheric environmentperformed on trial this time will be explained systematically.

(i) The corrosivity of the atmospheric environment is proportional to anannual wetness time TOW (h).

(ii) In a region where an annual mean wind speed W (m/sec.) is high, thewetness time TOW (h) is short because of a drying effect.

(iii) As an airborne salt amount C (mdd) increases, the corrosivity ofthe atmospheric environment increases.

(iv) As a sulfur oxide amount S (mdd) increases, the corrosivity of theatmosphere increases, but the influence of the sulfur oxide amount issmaller than that of the airborne salt amount.

(v) When the sulfur oxide amount S (mdd) increases in a region where theairborne salt amount C (mdd) is large, the corrosion inhibiting effectthanks to sulfur oxide is produced. It is thought that this is becausesulfate ions are adsorbed into rust, negatively charged rust is formed,and thereby the invasion of chloride ions is prevented.

(vi) Concerning the influence of an annual mean temperature T (K), therelation of Arrhenius, which is the basics of chemical kinetics, holds.

(vii) Assuming that in an inside girder (under a bridge girder), theatmospheric corrosion resistant steel is exposed, the rain's effect ofcleaning adherents is not expected.

When the atmospheric corrosivity index Z with respect to the atmosphericcorrosion resistant steel exposed under the bridge girder is formulatedbased on the aforementioned way of thinking, an equation (Eq. 6) isobtained.

$\begin{matrix}{Z = {\alpha \cdot {TOW} \cdot {\exp\left( {{- \kappa} \cdot W} \right)} \cdot \frac{C + {\delta \cdot S}}{1 + {ɛ \cdot C \cdot S}} \cdot {\exp\left( \frac{- E_{a}}{R \cdot T} \right)}}} & \left( {{Eq}.\mspace{14mu} 6} \right)\end{matrix}$

where α is a coefficient to make the value of the index Z within anumerical region of an order which is easy to handle and can bedetermined artificially. κ, δ, and ε are constants respectivelyrepresenting the degree of influence of each of factors which they areassociated with. R(J/K·mol)) is a gas constant. E_(a) is activationenergy of a corrosion reaction, and if reference is made to theconventional research results, for example, 5×10³ J/mol may besubstituted as a representing value.

The value of each of the influence degree constants κ, δ, and ε isfound, for example, in the following manner. First, the first-yearcorrosion amount A, the airborne salt amount C, and the sulfur oxideamount S of an SMA-type atmospheric corrosion resistant steel obtainedin the results of exposure tests of 41 bridges all over the countryregarding the atmospheric corrosion resistant steel conducted by thefollowing three: Public Works Research Institute of the Ministry ofConstruction; Japan Association of Steel Bridge Construction; and theKozai Club, and stipulated by JIS G 3114 are found. Additionally, theannual mean temperature T, an annual mean humidity RH, and the annualmean wind speed W in the neighborhood of each of places where theexposure tests are executed are found from weather data in 1999 which ismeasured and disclosed by each weather station. Moreover, the annualwetness time TOW is found from the annual mean temperature T and theannual mean humidity RH by a method by Kucera et al. (V. Kucera, J.Tidblad, A. A. Mikhailov: ISO/TC156/WG4-N314 Annex A, Mar. 30, 1990, theentire disclosure of which is incorporated herein by reference). Then,natural environmental conditions at each exposure test place arecalculated as the atmospheric corrosivity index Z by the equation (Eq.6), and the influence degree constants κ, δ, and ε are determined in thefollowing manner so as to obtain the best correlation with thefirst-year corrosion amount A. More specifically, initial values of theinfluence degree constants κ, δ, and ε which are regarded as appropriatein terms of chemical kinetics are inputted, and while the values ofthese three constants are systematically changed, an optimum solution ofa combination of the influence degree constants κ, δ, and ε whichminimizes a deviation in the correlation between the first-yearcorrosion amount A and the atmospheric corrosivity index Z is foundnumerically and analytically. The optimum values may be, for example,κ=0.1, δ=0.05, and ε=60.

The degree of influence on the first-year corrosion amount of theatmospheric corrosion resistant steel of various kinds of weatherfactors which have been hitherto considered to be unclarified naturalphenomena can be mathematically modeled as the corrosivity index Z forthe first time.

Based on the aforementioned data, the relation between the airborne saltamount C and the first-year corrosion amount A obtained by a methodhitherto performed is shown in FIG. 8. Moreover, the relation betweenthe corrosivity index Z calculated based on the equation (Eq. 6) and thefirst-year corrosion amount A is shown in FIG. 9 and FIG. 10 while beingclassified into a vertical exposure member and a horizontal exposuremember.

From a comparison between the graphs of FIG. 8 and FIG. 9 and acomparison between the graphs of FIG. 8 and FIG. 10, it can beascertained that the first-year corrosion amount A can be estimated witha far smaller error by a method of the present invention in which thevalue of the first-year corrosion amount A is found with the corrosivityindex Z than a conventional method in which the severity of corrosiveenvironment is represented by the airborne salt amount C only.

A horizontal specimen and a vertical specimen are different in asituation in which corrosive substances adhere to the surface thereof,whereby a difference in corrosion rate occurs inevitably. Thus, when aquadric regression analysis is performed with a first-year corrosionamount Av of the vertical exposure member and a first-year corrosionamount A_(H) of the horizontal exposure member with respect to thecorrosivity index Z shown in FIG. 9 and FIG. 10, equations, (Eq. 7a) and(Eq. 7b), are obtained. This means that the aforementioned F(Z) functioncan be found. Moreover, curves shown in FIG. 9 and FIG. 10 are curvesrepresented by the equations, (Eq. 7a) and (Eq. 7b), respectively.A _(v)(μm)=37.60Z ²+74.44Z+7.37 (p=7.64×10⁻³⁹)  (Eq. 7a)A _(H)(μm)=−24.16Z ²+182.19Z+4.05 (p=1.12×10⁻²³)  (Eq. 7b)

When, in this description, the numerical values regarding only thevertical exposure member and only the horizontal exposure member, ornumerical values regarding data obtained from only the vertical exposuremember and only the horizontal member are described distinctively, thedescription is given distinctively with symbols such as “A_(V)” and“A_(H)” corresponding to verticality (V) and horizontally (H). On theother hand, when verticality and horizontally are mixed or distinctionis unnecessary since verticality and horizontally are equal, thedescription is given with no distinction with symbols such as “A” and soon.

In each of the equation (Eq. 7a) and the equation (Eq. 7b), the value ofp used for a determination of significance of regression analysis isshown in parentheses. When the value of p is larger than 0.05, thisrelational expression is determined to be rejected by the nullhypothesis. However, since the value of p in each equation is extremelysmall, these regression analyses can be determined to be sufficientlysignificant statistically.

The first-year corrosion amount A found in each of the aforementionedequation (Eq. 7a) and equation (Eq. 7b) is a mean value, and hence it isinsufficient to show a prediction range. A weather data observation siteand a bridge construction site have different environmental conditions,whereby the occurrence of variations is inevitable. Hence,semilogarithmic plots in FIG. 9 and FIG. 10 are made to evaluate therange of the variations, and prediction results are presented in theform of a range with an upper value as 1.7 times as many as the meanvalue and a lower value as 1/1.7 times as many as the mean value, asshown in an equation (Eq. 8aU), an equation (Eq. 8aL), an equation (Eq.8bU), and an equation (Eq. 8bL).

$\begin{matrix}{A_{V}^{Upper} = {1.7A_{V}}} & \left( {{{Eq}.\mspace{14mu} 8}{aU}} \right) \\{A_{V}^{Lower} = {\frac{1}{1.7}A_{V}}} & \left( {{{Eq}.\mspace{14mu} 8}{aL}} \right) \\{A_{H}^{Upper} = {1.7A_{H}}} & \left( {{{Eq}.\mspace{14mu} 8}{bU}} \right) \\{A_{H}^{Lower} = {\frac{1}{1.7}A_{H}}} & \left( {{{Eq}.\mspace{14mu} 8}{bL}} \right)\end{matrix}$

The corrosivity index Z represents macro corrosivity of the atmosphericenvironment, whereas, in terms of the way of thinking, the values of thefirst-year corrosion amount A_(H) of the horizontal exposure member andthe first-year corrosion amount A_(V) of the vertical exposure memberare values corresponding to atmospheric corrosivity to the atmosphericcorrosion resistant steels placed under a horizontal exposure conditionand a vertical exposure condition, respectively. Returning to FIG. 6again and advancing the study in this sense allows a prediction thatsome relationship is obtained if a plot is made with the first-yearcorrosion amount A as the horizontal axis and the rust stabilizationindex B as the vertical axis.

Hence, if the aforementioned results of exposure tests of 41 bridges allover the country are plotted in this manner, a graph shown in FIG. 11 isobtained. From FIG. 11, the following tendency is perceived althoughthere are variations. Namely, within the range of the first-yearcorrosion amount A up to about 30 μm, the rust stabilization index Breduces, whereby the long-term effect of reducing the corrosion rate canbe expected. On the other hand, in the severe corrosive environment inwhich the first-year corrosion amount exceeds about 30 μm, the ruststabilization index B increases, whereby there is a tendency forabnormal corrosion to easily occur. Such a tendency is newly found out.It should be noted that FIG. 11 represents a basic concept in FIG. 6 forthe first time by quantitative data.

In the estimation of the rust stabilization index B, the inventor et al.of the present application seek related theories in which variations aresmaller while referring to weather data and the like, but they cannotobtain a better correlation than that in FIG. 11. Hence, a method forpredicting the rust stabilization index B is laid down with the thoughtthat FIG. 11 can be interpreted as follows.

(i) Variations in data can be interpreted as having occurred sincecorrosive factors such as the spraying of an antifreezing agent,deposition of dust or salt, which cannot be grasped by the measurementof corrosive environment exist, whereby a reduction in the ruststabilization index B is hindered. Hereinafter, such corrosive factorsare called excessive influence factors.

(ii) When the extent to which the excessive influence factors inhibitrust stabilization is extremely low, the rust stabilization index B iswithin a band in which 80% or more of measurement points aredistributed. Hereinafter, this state is called a natural state.

(iii) In the natural state, the probability that the rust stabilizationindex B exceeds a Natural Upper line is low.

(iv) In the natural state, the probability that the rust stabilizationindex B is lower than a Natural Lower line is low.

(v) When the excessive influence factors which cannot be grasped in theinitial environmental measurement act, it seems appropriate that anormal upper standard approximately at the level of influence in Japanis estimated to be a level shown by an Extra Influence line, but it isalso suitable to review and input again the measurement results of theenvironmental conditions and make a prediction calculation again underthe condition of the natural state. The level shown by the ExtraInfluence line is an excessive influence value of the rust stabilizationindex B and represented by a natural upper value of the ruststabilization index B plus 0.15. Hereinafter, the excessive influencevalue of the rust stabilization index B is called an excessive influenceB value, and the natural upper value of the rust stabilization index Bis called a natural upper B value. Similarly, a natural lower value ofthe rust stabilization index B is called a natural lower B value, anexcessive influence value of the first-year corrosion amount A is calledan excessive influence A value, and a natural upper value of thefirst-year corrosion amount A is called a natural upper A value.

According to the aforementioned interpretation, it is possible torepresent the range of the rust stabilization index B in the naturalstate estimated by using environmental data with the natural upper Bvalue and the natural lower B value. The excessive influence A value ispresumed to be approximately the natural upper A value, and thereby thevalue obtained by multiplying the natural upper A value by 1.0 isadopted as a normal standard. Moreover, the natural upper B value plus0.15 is adopted as a normal standard of the rust stabilization index Bin the excessive influence state. However, the degree of excessiveinfluence may change according to the circumstances, whereby it isnecessary to make a study while adjusting its value on the basis of thenatural upper A value and the natural upper B value. It should beunderstood that calculation by an excessive influence mode is a simplemethod only for indicating the standard as described above.

Since the value of A is a value corresponding to the first-yearcorrosion amount, it is possible from the above description to estimatethe value of A based on weather data, the amount of airborne salt, andthe amount of sulfur oxide. It is also possible to find the value of Aby an actual exposure test.

By setting the aforementioned distribution band of the first-yearcorrosion amount A and the rust stabilization index B, the result of theprediction calculation is also displayed in the form of a band. When thestatistical analysis of the amount of corrosion after 100 years iscarried out based on a result of statistically analyzing a predictionrange with the environmental conditions and a result predicted fromactual measurement data, it turns out that except for several caseswhere remarkable excessive influence exists, a natural upper line and anatural lower line of a predicted corrosion/wear curve coincide withabout 98% and 2% of a cumulative normal distribution curve,respectively. Hence, by adding a realization probability to thepredicted corrosion curve, the interpretation of a calculation resultcan be examined with higher accuracy.

Recently, new high-performance atmospheric corrosion resistant steelscalled coastal/seaside atmospheric corrosion resistant steels aredeveloped and introduced on the market by domestic steel manufacturers.Among them, only a coastal atmospheric corrosion resistant steel ofNippon Steel Corporation has long-term exposure data on conditions undera bridge girder. However, the number of pieces of data is smaller ascompared with that of a JIS type atmospheric corrosion resistant steel(hereinafter, steel materials stipulated by JIS G 3114 and JIS G 3125are collectively called a JIS type atmospheric corrosion resistantsteel), and it is difficult to grasp and analyze the correlation withthe aforementioned systematic weather data. However, at the present timewhen the influence of airborne salt on the seashore or caused by thespraying of an antifreezing agent is pointed out, it is desirable topresent a predicted value of the corrosion amount accumulated over timeas a standard in order to minimize the occurrence of defects of newsteel materials due to excessive expectation and safely realize LCCminimization. Therefore, a predicting method for a 3Ni-0.4Cu basedcoastal atmospheric corrosion resistant steel is laid down on a basis ofthe aforementioned method for predicting the corrosion amountaccumulated over time of the JIS type atmospheric corrosion resistantsteel in the following way of thinking.

The corrosion amount accumulated over time of the coastal atmosphericcorrosion resistant steel is subjected to an expression represented byY=AX^(B).

The coastal atmospheric corrosion resistant steel is a steel materialhaving lower corrosion and dissolution activity, whereby the first-yearcorrosion amount A of the coastal atmospheric corrosion resistant steelis smaller than that of the JIS type atmospheric corrosion resistantsteel.

The coastal atmospheric corrosion resistant steel is a steel in which areduction in pH at a corrosion interface is inhibited by the formationof Ni-containing rust (Zairyo-to-Kankyo, vol. 49, No. 1, pages 30–40(2000), the entire disclosure of which is incorporated herein byreference), and therefore the level of the rust stabilization index B ofthe coastal atmospheric corrosion resistant steel is lower than that ofthe JIS type atmospheric corrosion resistant steel.

When, based on the aforementioned way of thinking, the first-yearcorrosion amount A and the rust stabilization index B of the 3Ni-0.4Cubased coastal atmospheric corrosion resistant steel and the JIS typeatmospheric corrosion resistant steel (JIS-SMA490W;JIS G 3114) as acomparative example are found from the result of an exposure test undera bridge girder in which they are subjected to horizontal exposure fornine years at the quay in Kimitsu City where the amount of airborne saltis 1.3 mdd, the result in Table 1 can be obtained. Here, the 3Ni-0.4Cubased coastal atmospheric corrosion resistant steel is a steel material,for example, disclosed in Japanese Patent Application No. 2-125839,Japanese Patent Application No.11-172370, and “Zairyo-to-Kankyo, vol.49, No. 1, pages 30–40 (2000)”, the entire disclosure of which areincorporated herein by reference.

TABLE 1 parameter 3Ni-0.4Cu Steel JIS-SMA490W Ratio A(μm) 120 220 0.55 B0.72 0.95 0.76

From the result shown in Table 1, the first-year corrosion amount A ofthe 3Ni-0.4Cu based coastal atmospheric corrosion resistant steel is avalue obtained by multiplying the first-year corrosion amount A of theJIS-SMA atmospheric corrosion resistant steel by 0.55, and the level ofthe rust stabilization index B of the 3Ni-0.4Cu based coastalatmospheric corrosion resistant steel is a value obtained by multiplyingthe level of the rust stabilization index B of the JIS-SMA atmosphericcorrosion resistant steel by 0.76. Hence, based on this relation, theprediction of the corrosion amount accumulated over time as a standardis made. Incidentally, the result in Table 1 is the result of long-termexposure under such excessive influence conditions that, though it isexposure under a bridge girder, the scale is far smaller than that of anactual bridge, the dew condensation time is long, and that a largeamount of salt and dust is deposited. In a condition under an actualbride girder under which a good breeze is got and less deposits arecollected than under the aforementioned condition, the absolute valuesof both the first-year corrosion amount A and the rust stabilizationindex B are thought to be smaller. The ratio of the first-year corrosionamount A and the ratio of the rust stabilization index B between the JIStype atmospheric corrosion resistant steel and the 3Ni-0.4Cu basedatmospheric corrosion resistant steel cancel the aforementioned problemof absolute values due to the exposure condition, and hence they arethought to be effective. Incidentally, also as concerns the method forpredicting the corrosion/wear of the 3Ni-0.4Cu based atmosphericcorrosion resistant steel, the concrete method has been described here,but respective coefficients of other steel materials can be also foundby accumulating future data. It is possible to predict thecorrosion/wear of these new steel materials in the same manner, and itis needless to say that this case is also within the scope of thepresent invention.

According to the definition (proposal) of rust stabilization, in orderto further enhance the function by the surface treatment, it is far moreadvantageous to select a method for forming protective rust slowly andsurely than to accelerate corrosion to shorten the period of theformation of the protective rust. In other words, it is effective tomaintain the load carrying capacity of a structure over a very longperiod of time without repainting by the substitution for the protectiverust eventually while reducing the corrosion rate of the steel materialas low as possible, and as a result of the manifestation of thisfunction, the occurrence of outflow rust can be also prevented. From aresult of an exposure test over a period of 20 years to 30 years for theatmospheric corrosion resistant steel commercialized from long ago towhich a phosphoric acid based PVB based surface treatment method isapplied and application results of steel structures, it is proved thatthis concept can be realized.

The effect of the surface treatment for forming the protective rustslowly and surely can be provisionally estimated as a standard by thefollowing way of thinking.

(i) In the atmospheric corrosion resistant steel subjected to thesurface treatment for forming the protective rust slowly and surely,corrosion and wear are completely prevented until a step ofdeterioration of an organic coating is completed.

(ii) At the time when the step of deterioration of the organic coatingof the surface treatment for forming the protective rust slowly andsurely is completed, the protective film is formed on the surface of theatmospheric corrosion resistant steel by the effect of a protective filmformation promoter contained in a primer.

(iii) As a result, the corrosion rate of the atmospheric corrosionresistant steel at a point in time when the deterioration of the organiccoating has been completed is lower than that of the bare atmosphericcorrosion resistant steel at an early stage.

Information about the number of years the corrosion and wear of theatmospheric corrosion resistant steel have been completely prevented isnecessary to estimate the effect of the surface treatment applied to aregion under study based on the aforementioned qualitative hypothesis.Regarding this information, setting seems to change variously accordingto specifications of the surface treatment. With reference to remarksbased on actual results of steel materials manufacturers and surfacetreatment manufacturers, the number of years is inputted to software, sothat the effect can be provisionally estimated. Incidentally, the on-settime is determined during the deterioration period of the organiccoating, and at the same time, in view of the aforementioned effect, thecorrosion/wear curve is moved in parallel in the direction of anexposure period axis by the period of deterioration of the organiccoating of the atmospheric corrosion resistant steel subjected to thesurface treatment, so that the prediction of the corrosion amount withthe influence of the surface treatment taken into consideration becomespossible.

Moreover, by multiplying the predictively calculated first-yearcorrosion amount A and rust stabilization index B of the bareatmospheric corrosion resistant steel by a surface treatment effectcoefficient with respect to the first-year corrosion amount A and therust stabilization index B found from exposure data on the atmosphericcorrosion resistant steel subjected to the surface treatment, thecorrosion/wear curve of the surface treatment atmospheric corrosionresistant steel can be calculated. Thereby, also as concerns thefirst-year corrosion amount A and the rust stabilization index B, theprediction of the corrosion amount with the influence of the surfacetreatment taken into consideration can be realized.

When importance is attached to a landscape or when its application to aregion with severe corrosive environment is planned, surface treatmentor repainting is sometimes performed not only at an early stage but alsoevery several decades. Such a calculating method as enables theprediction of the long-term corrosion/wear amount in the aforementioneddesign which is predicated on repainting is premised on a concept thatthe corrosion rate is zero while a surface treatment film or a paintingfilm presents no problem, and the corrosion rate presents a propercorrosion rate in a state in which the surface treatment film or thepainting film is deteriorated.

According to an exemplary embodiment of the present invention, theminimum maintenance very long-term durability design of atmosphericcorrosion resistant steel structures which can contribute to animprovement in the financial standing of the nation or a localgovernment can be made with facility by a user who does not necessarilyhave a detailed knowledge of the complicated corrosion phenomenon of theatmospheric corrosion resistant steel. As a result, the provision ofsafe, secure, and low life-cycle cost infrastructure is furthered.Hence, potentiality which leads to the regeneration of industrialcompetitiveness of the entire nation increases. Prediction technology ofthe present invention, which is a new idea using a natural phenomenon ofthe corrosion of the atmospheric corrosion resistant steel, can beimproved to raise its precision with the further progress of the study.However, it is needless to say that even in this case, its basic portionis in the category of the present invention. When the results ofcalculation by the thus established method for predicting the long-termcorrosion loss of the atmospheric corrosion resistant steel was comparedwith hitherto accumulated actual exposure test data, it could beconfirmed that these two coincided well. It could be verified that thepredicting method of the present invention is appropriate.

It may need enormous labor and time to deal with calculation proceduresone by one when the aforementioned new way of thinking and the inventionbased thereon are executed. Hence, in order that everybody can easilypredict the long-term corrosion/wear amount of the atmospheric corrosionresistant steel with a personal computer, the effective and efficientmanifestation of the aforementioned significance is tried by developingcalculatable software with VISUAL BASIC (registered trademark) 6.0 ofMICROSOFT (registered trademark) Corporation as a language.

Software according to one of exemplary embodiment of the presentapplication can be used to implement the method(s) according to thepresent invention using the system according to the present invention.

First, in a panel (screen) of “Atmospheric corrosion resistant steelUsage Environment Overview” shown in FIG. 12, environmental conditionsare set. In an environmental condition setting screen, weather data andairborne salt/sulfur oxide data of a desired region are inputted, aregion/spot name and its neighboring meteorological observatoryinformation are inputted, and a condition file (.YSK) is created andstored by a menu operation. Moreover, the storage place and name of anoutput file (.CSV) to which the prediction result is outputted are set.

It should be mentioned that the wetness time TOW and the atmosphericcorrosivity index Z are automatically calculated from input data.Moreover, the annual precipitation is not used in the calculation ofthis software, but it is desirable to input and store it as a referencevalue. As for the airborne salt amount and the sulfur oxide amount, iftheir measurement values can be obtained, the values are inputted. Whentheir measurement values cannot be obtained, it is possible to click acheckbox and set an approximate value from five levels in Japan as anassumed value. When the prediction result is used for the design of anactual structure or the like, it is thought that the condition settingincluding a judgment about whether or not to use this software isaccompanied by its appropriate accountability. Therefore, the name of aperson who sets the conditions is entered. When the corrosion amount forone year is known by actual exposure, the prediction calculation basedon the actually measured first-year corrosion amount A can be performedby inputting the first-year corrosion amount A by the menu operation ofthis screen and switching mode setting.

The values of longitude and latitude of a construction side arerepresented by decimal conversion of fractions smaller than a degree.For display or input in degree, minute, and second, an “Input” button isclicked to display a panel shown in FIG. 13. A selection between eastlongitude and west longitude, a selection between north latitude andsouth latitude, and an input of the values of the degree, minute, andsecond are made, and then if a “=” button is clicked, the value obtainedby the decimal conversion of fractions smaller than the degree iscalculated and displayed. Further, when a “result transfer” button isclicked, an input operation of data on latitude and longitude iscompleted.

The weather data can be also set easily. Setting values can be easilyinputted from a database to a text box shown in the screen of theaforementioned “Atmospheric corrosion resistant steel Usage EnvironmentOverview” by clicking data processing and “Visual Climate Search (notshown)” by the menu operation to activate a panel shown in FIG. 14. Onthis occasion, if the latitude and longitude of a spot under study areinputted in advance, a database selection operation becomes moreefficient. A small red circle is shown at a point corresponding to thelatitude and longitude inputted in advance on a map of the VisualClimate Search. A range is displayed by a mouse operation within themap, and meteorological observatories can be narrowed down to thosewithin the range. If meteorological observatories in the vicinity of theread circle mark are extracted and thereafter one is selected from alist box, its latitude and longitude are shown on the map, and thedistance modulus is calculated and displayed. The smaller the distancemodulus, the smaller differences in latitude and longitude are.

The distance modulus indicates differences in latitude and longitude ina plane, and thereby referring to the altitude of the weatherobservation site, the selection operation is advanced. When a “datatransfer” button is clicked, selected weather conditions areautomatically inputted to the screen of the “Atmospheric corrosionresistant steel Usage Environment Overview”. Note that this panel isdevised so that weather data within Japan can be easily inputted, andthe setting of weather conditions necessary for calculation can be alsoinputted manually. Namely, the prediction of long-term corrosion/wear ofthe atmospheric corrosion resistant steel in overseas countries ispossible, and the effect of the present invention is not limited withinJapan, and in fact can be utilized throughout the world.

Before executing calculation, the excessive influence degree isconfirmed by a panel shown in FIG. 15. General values of a scalingfactor with respect to the natural upper A value and a value added tothe natural upper B value are shown by default. In a case where verystrong excessive influence is predicted or the like, these values shouldbe set a little larger in some cases. The predicting method with theexcessive influence degree which was not included in the environmentalmeasurement value taken into account seems to be unnecessary since aprediction calculation in a natural state based on proper measurementresults needs to be originally made, but when the environment seems tobe severer than the early stages of construction in maintaining andmanaging the actual bridge, it is thought that it is a convenientfunction to display an empirical standard value. Therefore, the functionof changing the excessive influence degree is added to this software.After all the condition setting input is completed, the “dataprocessing” is selected by the menu operation, and then “ExecuteCalculation of Value A and Value B” is selected to move to a screen of“Parameter Calculation results”. Then, “to Secular Prediction” isselected by the menu operation, and by clicking “Execute Calculation”, apanel of “Secular Corrosion Prediction Overview” is displayed.

In the panel of Parameter Calculation Results (Assumption of BridgeInside Girder) shown in FIG. 16, the estimated results of the first-yearcorrosion amount A and the rust stabilization index B can be seen. Thecorrosion and wear of the atmospheric corrosion resistant steel arepredicted by an expression represented by Y=AX^(B) (Y: one-sidedcorrosion amount accumulated over time, X: number of years elapsed)which is generally accepted. In the panel of “Parameter CalculationResults”, estimated values of the first-year corrosion amount A and therust stabilization index B based on the setting conditions aredisplayed. The prediction range in a state in which the extent to whichthe rust stabilization is inhibited by excessive influence factors suchas the influence of spraying of the antifreezing agent, deposition ofsalt, and retention of condensation water is very low is displayed witha natural lower value (cumulative normal value 2% value) and a naturalupper value (cumulative normal probability 98% value). The standardvalue when the extent to which the rust stabilization is inhibited bythe excessive influence factors is large is displayed at the same time.A shift to a panel of “Calculation Results Overview Reference” is madeby the menu operation or clicking a button of “Next”.

Based on constant prediction values displayed in the previous panel, 2%,50%, and 98% probability values of the one-sided corrosion/wearprediction values of each condition of the atmospheric corrosionresistant steel (SMA) and the coastal atmospheric corrosion resistantsteel (3Ni-0.4Cu) after 10 years, 50 years, and 100 years, under thehorizontal or vertical exposure condition are calculated. The results ofthis calculation can be seen in a panel shown in FIG. 17.

When a button at the lower end of the panel of “Secular corrosion AmountPrediction Overview” is clicked, a corrosion curve predicted by thecalculation can be displayed in graphical form as shown in FIG. 18. Ahatched region in the graph is a predicted region of corrosion and wear(range of 2σ) in the natural state, and this range is further dividedinto regions of 1σ, 0.5σ, and 0.25σ, which are displayed. Namely, it ispossible to add the realization probability to the predictedcorrosion/wear curve and display (represent) it. Also in the followingFIG. 19, FIG. 20, FIG. 21, FIG. 22, FIG. 24, FIG. 26, and FIG. 27, it ispossible to add the realization probability to the predictedcorrosion/wear curve and display (represent) it. Display/non-display ofa desired probability region can be reset by operating a checkbox at thelower left. According to arguments in recent academic conferences,concerning both concrete and steel, design and maintenance managementneed to be performed on the assumption that corrosion and deteriorationoccur on a long-term basis. Moreover, as for structures to beconstructed, there is such a movement that a plan of maintenancemanagement ought to be formed from the stage of designing.

Based on the calculation results of this software, application policiesof steel materials and a surface treatment method, the design ofbridges, and maintenance management policies are required to be studiedso that the corrosion amount can be limited to within approximately 0.3mm on one side in 50 years and 0.5 mm on one side in 100 years, thiscorrosion amount hardly affecting the load carrying capacity andusability of steel bridges. In the calculation example in FIG. 18, it isdetermined that when a bare horizontal member of the JIS typeatmospheric corrosion resistant steel (SMA-Horizontal) is used underthese environmental conditions, there is a possibility of exceeding acorrosion amount of 0.5 mm in 100 years at a probability of about 30%.Hence, a prediction calculation is made with 3Ni-0.4Cu based costalatmospheric corrosion resistant steel as a steel material, the resultexemplified in FIG. 19 is obtained. Incidentally, a calculated valuewith excessive influence taken into consideration is also shown by avertically hatched region. From this result, if the steel material isthe 3Ni-0.4Cu based coastal atmospheric corrosion resistant steel,minimum maintenance is judged to be sufficiently possible in the use ofthe bare atmospheric corrosion resistant steel under these environmentalconditions.

For the purpose of further inhibiting the corrosion of the atmosphericcorrosion resistant steel and the coastal atmospheric corrosionresistant steel, a surface treatment method which promotes ruststabilization slowly and surely is sometimes used, whereby a list box isset up at the lower right of a panel in preparation for the need forestimating roughly its effect as a corrosion amount. If an assumedperiod until the surface treatment film deteriorates and the corrosionof the atmospheric corrosion resistant steel or the coastal atmosphericcorrosion resistant steel starts under these usage conditions isselected, the secular corrosion amount prediction curve is recalculatedas shown in FIG. 19 in the case of JIS type atmospheric corrosionresistant steel subjected to general painting surface treatment, and asshown in FIG. 20 in the case of the JIS type atmospheric corrosionresistant steel subjected to surface treatment for atmospheric corrosionresistant steel.

The former shown in FIG. 19 is a corrosion/wear prediction curveobtained by making a calculation with the start time of corrosion of thesteel material as after 25 years on the assumption that the treatmentfor promoting the formation of protective rust is not performed. On theother hand, the latter shown in FIG. 20 is a corrosion/wear predictioncurve obtained by making a calculation with the start time of corrosionas after 25 years and simultaneously multiplying a coefficient of effecton the first-year corrosion amount A and the rust stabilization index Bon the assumption that the treatment for promoting the formation ofprotective rust is performed. From these calculation results, under thisenvironment, it can be determined that 100-year service life can berealized by minimum maintenance by subjecting the JIS type atmosphericcorrosion resistant steel to surface treatment which promotes theformation of the protective rust.

Repainting in surface treatment for the atmospheric corrosion resistantsteel is not generally expected, but in this software, to answerpurposes and needs such as the realization of very long-term durabilityat low cost under severe corrosive environment, use of surface treatmentfor landscape specifications, an increase in life combined withpainting, and the like, the calculation of the corrosion/wear curve whenrepainting is permitted is also possible. When a “Repeat” button isclicked after the number of durable years of the surface treatment filmis inputted in the screen in each of FIG. 18 to FIG. 21, a panel whichencourages an input of a grace period before repainting is displayed.The default is ten years, but a change is possible between zero years to60 years. For example, when the durability of a general surfacetreatment film is set to 25 years and the grace period before repaintingis set to five years, this software is so programmed that acorrosion/wear curve of a total of 30 years is repeated in an additionalmanner, and as a result, a corrosion/wear prediction curve as a standardup to 100 years may be ascertained. The result of this is shown as inFIG. 22. From FIG. 22, it can be determined that when general surfacetreatment is performed for the atmospheric corrosion resistant steelunder these environmental conditions, 100-year service life can berealized if a design and a maintenance management policy on theassumption of repainting are made.

In the aforementioned examples of corrosion/wear prediction, calculationis made by inputting conditions as macro representatives of constructionenvironment, but in an actual structure which has a complicated shapeand extends over a wide range, environmental conditions are differentfrom one portion of the structure to another. Accordingly, the need forimproving prediction precision by ascertaining environmental conditionsaccording to each portion of a structure, and studying a corrosionprotection designing method according to each portion of the structureis pointed out.

FIG. 23 is an example of conditions inputted to a panel of “UsageEnvironment Conditions Setting” in a portion of a structure around whichthe amount of airborne salt is assumed to be relatively small in abridge structure to be constructed. Such conditions can hold in generalgirder surfaces which are not directly exposed to a sea wind in thebridge.

FIG. 24 is an example of a corrosion/wear prediction curve calculatedunder the conditions in FIG. 23 in the portion of the structure aroundwhich the amount of airborne salt is assumed to be relatively small. Theprecision of a prediction calculation rises by a rise in the precisionof setting of environmental conditions according to each portion of astructure, so that a region up to 0.5σ is displayed. From thisprediction result, it is determined that 100-year durability can befully realized even if the bare JIS type atmospheric corrosion resistantsteel is used for these general girder surfaces.

FIG. 25 is an example of conditions inputted to the panel of “UsageEnvironment Conditions Setting” in a portion of the structure aroundwhich the amount of airborne salt is assumed to be relatively large andthe humidity is assumed to be high in the bridge structure to beconstructed. Such conditions can hold in girder end portions or the likewhich are structurally poorly ventilated with a tendency of highhumidity.

FIG. 26 is an example of a corrosion/wear prediction curve calculatedunder the conditions in FIG. 25 in the portion of the structure aroundwhich the amount of airborne salt is assumed to be relatively large andthe humidity is assumed to be high. Also in this case, the precision ofsetting of environmental conditions rises, so that as concerns theprediction curve, a region up to 0.5σ is displayed. From this predictionresult, it turns out that even in the same construction object, thecorrosive environment is sometimes locally severe, so that if a portionof the structure under the severe environment is barely used, corrosionexcessively progresses, which causes a problem. There is a possibilitythat a minimum maintenance structure can be realized by taking somecorrosion protection measure against only such a portion of thestructure.

FIG. 27 is an example of a corrosion/wear prediction curve calculatedalso under the conditions in FIG. 25 in the portion of the structurearound which the amount of airborne salt is assumed to be relativelylarge and the humidity is assumed to be high and which is subjected torust stabilization surface treatment for the atmospheric corrosionresistant steel. Based on this prediction result, it can be determinedthat very long-term durability can be realized at the lowest cost as theentire structure if only a portion of the structure under the locallysevere corrosive environment is subjected to the rust stabilizationsurface treatment. Accordingly, it becomes possible to reflect thisknowledge in the design from the beginning. Similarly, as for existingstructures, it is also possible to make a prediction on future corrosionand wear on a portion-by-portion basis and draw up a maintenancemanagement policy.

If a calculation method for predicting the long-term corrosion/wearamount of the painted atmospheric corrosion resistant steel which isimplemented in the form of software as described above can be widely andgenerally used, is possible to (i) determine the applicability of theatmospheric corrosion resistant steel, (ii) select a steel type, (iii)select a surface treatment method, (iv) make a durable design, (v) drawup a maintenance management policy, and so on at any given constructionsite, which is not limited within any country, by referring to itsoutput data. Consequently, understanding of the proper usage of theatmospheric corrosion resistant steel is spread, which contributes to anincrease in the reliability of this steel material. Moreover, theprovision of safe, secure and low life-cycle cost infrastructure isfurthered. Also, by a comparison with the predicted calculation result,research and development on new atmospheric corrosion resistant steelmaterials and the surface treatment and maintenance management methodtherefor are made more efficient, and moreover it is needless to saythat the predicted calculation result can be effectively utilized forthe setting of a new development goal. Its utilization inevitably leadsto a great increase in the efficiency of a business method concerningthe atmospheric corrosion resistant steel and the surface treatmenttherefor.

Moreover, the following business form can be realized by using softwarecapable of carrying out the method according to the present invention.

First, in the stage of planning a steel structure to which theatmospheric corrosion resistant steel is applied (the stage of selectinga steel type), it is possible to plan the type of steel applied to thesteel structure through the steps of: calculating a predicted corrosionamount of one type or more than one type of atmospheric corrosionresistant steel as a candidate based on numerical values obtained byactually measuring or estimating environmental data including an annualmean temperature, humidity, precipitation, wind direction/speed,airborne salt amount, sulfur oxide amount, and so on in a plannedlocation for use where a user plans to use the atmospheric corrosionresistant steel by the method of the present invention; and comparingthe predicted corrosion amount and a design permissible corrosion amountin a design life period. In other words, it is possible to select asteel type through the calculation of a predicted corrosion amount ofthe aforementioned each atmospheric corrosion resistant steel withextrinsic corrosion information including weather observation data, anamount of airborne salt, and an amount of sulfur oxide in the plannedlocation for use where the atmospheric corrosion resistant steel is tobe used, and intrinsic corrosion information on components of one ormore than one type of atmospheric corrosion resistant steel planned tobe used, and the comparison of the aforementioned predicted corrosionamount and the design permissible corrosion amount in the design lifeperiod.

In this determination of applicability, generally, when the predictedcorrosion amount of the atmospheric corrosion resistant steel is equalto or smaller than the permissible corrosion amount in the comparisonbetween the predicted corrosion amount and the permissible corrosionamount, this atmospheric corrosion resistant steel is regarded as anapplicable steel type, but in some cases, for example, when a largeamount of thawing salt is sprayed to prevent the road surface fromfreezing, excessive influence factors need to be taken intoconsideration.

In such case, it is suitable that in the comparison between thepredicted corrosion amount and the permissible corrosion amount, thedifference between them is set to be a given specified amount or moreaccording to the excessive influence factors, and it is preferable toincorporate this in the exemplary predicting method according to thepresent invention as a correction for rust stabilization factors.

It is preferable that this planning method or selection method furtherincludes the steps of: regarding a steel type whose predicted corrosionamount exceeds the permissible corrosion amount, recalculating apredicted corrosion amount after adding a corrosion protection methodand/or a maintenance management method capable of reducing the predictedcorrosion amount to the permissible corrosion amount or less; anddisclosing an expected cost and an expected life to a user when one typeor more than one type of atmospheric corrosion resistant steel as acandidate is applied to a spot and a portion of a structure to be usedby the user. Namely, regarding the steel type whose predicted corrosionamount exceeds the permissible corrosion amount, it is preferable tocalculate a predicted corrosion amount when at least one type of methodselected from the group consisting of a corrosion protection method anda maintenance management method for reducing the predicted corrosionamount. Moreover, it is preferable to obtain an expected cost and anexpected life when the one or more than one type of atmosphericcorrosion resistant steel is used in the planned location for use. Thisis because the cost including surface treatment and the like, life, andso on can be also simultaneously considered.

Next, in the maintenance management of the steel structure, it ispossible to calculate first-year corrosion amounts A_(V) and A_(H) basedon actual measurement of corrosion losses after a lapse of any givenperiod of time, and based on the predicted corrosion amount recalculatedfrom the actually measured first-year corrosion amounts by the method ofpresent invention, to determine a more appropriate future maintenancemanagement policy. In other words, it is possible to calculate actuallymeasured first-year corrosion amounts of a vertical exposure member anda horizontal exposure member made of an atmospheric corrosion resistantsteel respectively based on measurement results of corrosion losses inany given period of time of the vertical exposure member and thehorizontal exposure member made of the atmospheric corrosion resistantsteel, calculate a predicted corrosion amount of the atmosphericcorrosion resistant steel with extrinsic information including weatherobservation data, an amount of airborne salt, and an amount of sulfuroxide in a planned location for use where the atmospheric corrosionresistant steel is to be used, intrinsic corrosion information oncomponents of the atmospheric corrosion resistant steel, and therespective actually measured first-year corrosion amounts, and determinethe maintenance management policy based on the predicted corrosionamount.

In this case, it is preferable that the recalculation is coefficientcorrection in the corrosivity index Z. Namely, it is preferable tocalculate the corrosivity index Z with the under mentioned equation (Eq.6) when the predicted corrosion amount is calculated.

When an actual measured value exceeds a predicted value with regard toA_(V) and/or A_(H), it is preferable to adopt a maintenance managementpolicy in which the future predicted corrosion amount becomes equal toor less than a predicted corrosion amount at the beginning of planing.More specifically, when at least one of the actually measured first-yearcorrosion amounts of the vertical exposure member and the horizontalexposure member made of the atmospheric corrosion resistant steelexceeds the predicted corrosion amount, it is preferable to adopt such amaintenance management policy that the predicted corrosion amountbecomes smaller than a value at the beginning of planning. However, itis preferable to determine the amount of an excess when the managementpolicy is actually changed in consideration of the absolute value of thecorrosion amount and so on.

A more appropriate maintenance management policy includes the change ofa portion of a structure subjected to one type or more than one type ofoperation out of inspection, repair, and cleaning and/or the timing ofperforming the operation from originally planed ones. It should be notedthat the maintenance management policy is not limited to the above.

Moreover, in an exemplary method for providing information on theatmospheric corrosion resistant steel, as an example thereof is shown inFIG. 28, a method for providing information on an atmospheric corrosionresistant steel, including the steps of: a user accessing a servercapable of performing the method of the present invention via anelectric communication line such as the Internet and inputtingenvironmental data including an annual mean temperature, a humidity, aprecipitation, a wind direction/speed, an amount of airborne salt, andan amount of sulfur oxide in a spot and a portion of a structure towhich the user plans to apply the atmospheric corrosion resistant steel,based on actually measured or estimated numerical values; calculating apredicted corrosion amount of one type or more than one type ofatmospheric corrosion resistant steel as a candidate based on the inputand the selection of a steel type which the user plans to use accordingto the method of the present invention; and displaying a result of thecalculation in a terminal of the user via the electric communicationline such as the Internet, becomes possible. In other words, theprovision of information including the steps of: a user accessing aserver for calculating a predicted corrosion amount of an atmosphericcorrosion resistant steel with environmental data including weatherobservation data, an amount of airborne salt, and an amount of sulfuroxide, and intrinsic corrosion information on components of theatmospheric corrosion resistant steel from a terminal device via anelectric communication line; the user inputting environmental dataincluding weather observation data, an amount of airborne salt, and anamount of sulfur oxide in a planned location for use where anatmospheric corrosion resistant steel is to be used from the terminaldevice to the server; the user permitting the server to recognizeintrinsic corrosion information on components of one or more than onetype of atmospheric corrosion resistant steel planned to be used fromthe terminal device; the server calculating a predicted corrosion amountof each of the atmospheric corrosion resistant steels based on theenvironmental data and the intrinsic corrosion information; the servertransmitting the predicted corrosion amount to the terminal device viathe electric communication line; and the terminal device outputting thepredicted corrosion amount from the terminal device, becomes possible.

It is one of preferable embodiments that such information is provided aspart of a homepage of a steel materials manufacturer. By providing suchinformation, a user can investigate whether an atmospheric corrosionresistant steel can be actually used in a spot and a portion of astructure to which the user plans to apply the atmospheric corrosionresistant steel on the Internet. As a result, this becomes very usefulinformation disclosure to diffuse the atmospheric corrosion resistantsteel.

It is preferable that the user can select a steel type whose predictedcorrosion amount is to be calculated by preparing a window in which theenvironmental data on the spot and the portion of the structure to whichthe user plans to apply the atmospheric corrosion resistant steel isinputted for access from the user and displaying steel types which thesteel materials manufacturer can provide by a menu selection method inthis window. This improves user-friendliness and facilitates thearrangement of data when the data is stored in the server.

Further, the environmental data inputted by the user is preferably amean temperature, humidity, wind direction/speed, and so on actuallymeasured in the spot and the portion of the structure to which the userplans to apply the atmospheric corrosion resistant steel in view of thefact that the aforementioned data provides the steel materialsmanufacturer with useful information as data on calculation precision ofthe predicted corrosion amount and steel materials environment.

However, on the other hand, it is naturally assumed that there are manyusers which have access without the aforementioned preparation, andhence it is preferable for convenience of the user that the step ofacquiring part or all of environmental data necessary for calculation ina manner other than the aforementioned input is further included. Inother words, it is preferable that the step of the server acquiring atleast part of elements constituting the environmental data in a mannerother than the input by the user is further included. For example, suchan embodiment that clicking a location for use of a steel material on amap links to a database of the Meteorological Agency or the like andthereby necessary environmental data can be retrieved or calculated ispreferable.

Furthermore, since it is open to an unspecified number of users, it ispreferable that an access right in the server is hierarchized, and thatan access right for a user ID to access the server is set according to ausage record of the atmospheric corrosion resistant steel of the user.

If the environmental data inputted by the user is stored in the serverand can be seen from the server administration side, it becomes possibleto determine a business counterpart based on user IDs which got accessto the server or the frequency of access by using the data, analyze theenvironmental data inputted by the user and stored and accumulated inthe server, and based on a result thereof, enlarge the environment towhich existing steel types are applied and perform research anddevelopment on new steel types.

Additionally, if the user is provided with further detailed informationin addition to calculation results obtained by access from the user tothe server when there is a request from the user and/or when specialconsideration to the inputted environment is necessary, it is morepreferable in terms of the user's convenience and prevention of wronguse of the steel type.

In this case, it is efficient and desirable to transfer the detailedinformation to a terminal installed in the user's nearest business basevia an electric communication line such as the Internet. The nearestbusiness base includes a place of the user to which a person in chargeof business goes. Namely, the detailed information may be transferred tothe terminal installed in the user's nearest business base or may betransferred to a portable terminal brought into the place of the user.

In a situation of a business operation in front of the user, in thestudy of application of an atmospheric corrosion resistant steel to aspot and a portion of a structure to which the user plans to apply theatmospheric corrosion resistant steel, a form of business for anatmospheric corrosion resistant steel including the steps of: a personin charge of business inputting environmental data including an annualmean temperature, a humidity, a precipitation, a wind direction/speed,an amount of airborne salt, and an amount of sulfur oxide in the spotand the portion of the structure to which the user plans to apply theatmospheric corrosion resistant steel based on actually measured orestimated numerical values to a computer capable of executing the methodof the present invention via an electric communication line such as theInternet or in a stand-alone system; calculating a predicted corrosionamount of one type or more than one type of atmospheric corrosionresistant steel as a candidate by the method of the present inventionaccording to the aforementioned input and the selection of the steeltype which the user plans to use; and presenting a result of thecalculation to the user, becomes possible.

In other words, a business for an atmospheric corrosion resistant steel,including the steps of: a person in charge of business inputtingextrinsic corrosion information including weather observation data, anamount of airborne salt, and an amount of sulfur oxide in a plannedlocation for use where a customer plans to use an atmospheric corrosionresistant steel to an electronic calculator for calculating a predictedcorrosion amount of an atmospheric corrosion resistant steel withextrinsic corrosion information including weather observation data, anamount of airborne salt, and an amount of sulfur oxide and intrinsiccorrosion information on components of the atmospheric corrosionresistant steel; the person in charge of business permitting theelectronic calculator to recognize intrinsic corrosion information oncomponents of one or more than one type of atmospheric corrosionresistant steel which the customer plans to use; the electroniccalculator calculating a predicted corrosion amount of each of theatmospheric corrosion resistant steels; and the person in charge ofbusiness presenting a result of the calculation by the electroniccalculator to the customer becomes possible.

Also in this case, it is preferable for convenience that the step ofacquiring or calculating part or all of environmental data necessary forcalculation in a manner other than the aforementioned input is furtherincluded. Moreover, regarding a steel type whose predicted corrosionamount exceeds a permissible corrosion amount, it is very desirable thatthe step of recalculating a predicted corrosion amount after a corrosionprotection method and/or a maintenance management method such as canreduce the predicted corrosion amount to the permissible corrosionamount or less is added and the step of disclosing an expected cost andan expected life when one type or more than one type of atmosphericcorrosion resistant steel as a candidate is applied to a spot and aportion of a structure in which the user uses it, are further includes,since the cost including surface treatment and so on, the life, and thelike can be studied at the same time.

Also in this business form, a terminal capable of performing thecalculation by the method of the present invention may be located in abusiness department or a person in charge of business may take such aportable terminal to a place of the user. Preferably, if access toweather data and so on disclosed by the Meteorological Agency from thisterminal is possible, a concrete study based on data can be made on thespot during consultation on the selection of a steel material even whenthe user does not keep data such as temperature on hand.

According to this exemplary business method according to the presentinvention, not only the business operation can be made more efficient,but also a large merit that steel types as candidates can be promptlyand quantitatively compared can be provided to the user. Besides, thisprompt provision of quantitative data enhances understanding of theadded value of a steel material called atmosphere corrosion resistancewhich conventionally has many uncertain factors and leads to furtherdiffusion of the atmospheric corrosion resistant steel.

INDUSTRIAL APPLICABILITY

According to a method of the present invention, the amount of corrosionin a service life of several decades can be predicted with highprecision even based on limited actual measurement data such as anexposure test. Moreover, it is also easy to incorporate a corrosionprotection method and a maintenance management method therein.

The present invention can make various operations such as judgment onthe applicability of an atmospheric corrosion resistant steel, selectionof a material, durability design, judgement on the applicability ofsurface treatment and selection of its type, and creation of amaintenance management policy, which hitherto rely on a long-termexposure test, more precise and more efficient. Moreover, the presentinvention can reduce the cost of the business operation of theatmospheric corrosion resistant steel. Accordingly, the presentinvention can contribute to a rise in the competitiveness of theatmospheric corrosion resistant steel.

Conventionally, the judgment on the applicability has been made only bythe amount of airborne salt, whereby in some region, the application ofthe atmospheric corrosion resistant steel is withheld even though it isa region where maintenance and management costs can be originallyreduced by using the atmospheric corrosion resistant steel, which causesan increase in construction client's maintenance and management costs.Contrary to this, repair costs are sometimes caused since abnormalcorrosion unexpectedly occurs due to high humidity and temperature orthe like even though the amount of airborne salt is small. According tothe present invention, it is possible to avoid such situationsbeforehand.

Such avoidance of problems prevents troubles when the atmosphericcorrosion resistant steel is used which are probably caused by theexistence of uncertain factors on the environment side. Accordingly, thepresent invention fulfills a role in maintaining an infrastructuresafely and securely. It becomes possible to design a structuremanufactured of an atmospheric corrosion resistant steel having a morethan 100 year-service life by a combination of these series of long-termcorrosion/wear predictions and various kinds of corrosion protectionmethods based on obtained calculation results. Consequently, therealization of minimum maintenance of an infrastructure is enhanced.

1. A method comprising: measuring or obtaining TOW, an annual wetnesstime (h) in a location; measuring or obtaining W, an annual mean windspeed (m/sec.) in the location; measuring or obtaining C, an airbornesalt amount (mdd) in the location; measuring or obtaining S, a sulfuroxide amount (mdd) in the location; measuring or obtaining T, an annualmean temperature (K) in the location; determining a corrosivity index Zof an atmospheric corrosion resistant steel at the location where theatmospheric corrosion resistant steel is to be used; determining acorrosion amount of the atmospheric corrosion resistant steel using thecorrosivity index Z; and selecting a steel type for a steel structure,or designing or maintaining the steel structure based on the determinedcorrosion amount, wherein the corrosivity index Z is determined usingthe following equation $\begin{matrix}{Z = {\alpha \cdot {TOW} \cdot {\exp\left( {{- \kappa} \cdot W} \right)} \cdot \frac{C + {\delta \cdot S}}{1 + {ɛ \cdot C \cdot S}} \cdot {\exp\left( \frac{- E_{a}}{R \cdot T} \right)}}} & \;\end{matrix}$ where Ea is activation energy (J/mol) of a corrosionreaction of the atmospheric corrosion resistant steel, R is a gasconstant (J/K(K·mol)), α is a coefficient constant, and κ, δ, and ε areinfluence degree constants.
 2. The method according to claim 1, furthercomprising a substep of determining a corrosion amount accumulated overtime of the atmospheric corrosion resistant steel by estimating afirst-year corrosion amount and a rust stabilization index of theatmospheric corrosion resistant steel from the corrosivity index Z. 3.The method according to claim 1, further comprising a substep ofestimating a first-year corrosion amount A_(V) of a vertical exposuremember and a first-year corrosion amount A_(H) of a horizontal exposuremember from the corrosivity index Z by a quadratic regression analysis.4. The method according to claim 3, further comprising finding arelational expression based on the following equations:A _(V)(μm)=37.60Z ²+74.44Z+7.37 (p=7.64×10⁻³⁹)A _(H)(μm)=−24.16Z ²+182.19Z+4.05 (p=1.12×10⁻²³).
 5. The methodaccording to claim 3, further comprising determining a range ofvariations by multiplying estimated values of the first-year corrosionamounts A_(V) and A_(H) by each of respective constants which correspondto an upper limit and a lower limit of said range of variations.
 6. Themethod according to claim 5, wherein each upper or lower limit of therange of variations is determined by using one of: taking an upper limitA^(Upper) _(V) of a range of the first-year corrosion amount A_(V) asthe following equation: A_(V) ^(Upper)=1.7A_(V); taking a lower limitA^(Lower) _(V) of the range of the first-year corrosion amount A_(V) asthe following equation: ${A_{V}^{Lower} = {\frac{1}{1.7}A_{V}}};$ takingan upper limit A^(Upper) _(H) of a range of the first-year corrosionamount A_(H) as the following equation: A_(H) ^(Upper)=1.7A_(H); andtaking a lower limit A^(Lower) _(H) of the range of the first-yearcorrosion amount A_(H) as the following equation:$A_{H}^{Lower} = {\frac{1}{1.7}{A_{H}.}}$
 7. The method according toclaim 3, further comprising, based on the first-year corrosion amountsA_(V) and A_(H) and a distribution function of a rust stabilizationindex: taking an upper limit of a region where 80% or more ofmeasurement points are distributed as a natural upper rust stabilizationindex or as an excessive influence rust stabilization index obtained byadding a value according to the degree of excessive influence to thenatural upper rust stabilization index; taking a lower limit of theregion where 80% or more of the measurement points are distributed as anatural lower rust stabilization index; and taking a value obtained byadding 0.15 to the natural upper rust stabilization index as theexcessive influence rust stabilization index.
 8. The method according toclaim 1, wherein the determined corrosion amount is used to select asteel type for a steel structure.
 9. The method according to claim 1,wherein the determined corrosion amount is used to design a steelstructure.
 10. The method according to claim 1, wherein the determinedcorrosion amount is used to maintain a steel structure.